The line comes from Star Wars: Episode V - The Empire Strikes Back, released in 1980, when Darth Vader confronts Luke Skywalker during their lightsaber duel on Cloud City. In the film Vader actually says 'No, I am your father,' although the version with Luke's name added has become the version most people quote. The reveal was kept secret from most of the cast and audience before release, which helped it become one of cinema's most repeated twists. It spread through television, parody, and later through memes and short videos, where it now signals any sudden, dramatic revelation.